Math Whiz? Answer this please

The site that gave us the grammar and Spelling quizes also had one for math.

I'd like to know how to answer this one question please:

The Washington Monument is 555 feet tall. For a class project, Tom is to make a scale model of the monument to place in the front hall display case. The display case is 24 inches tall. Which scale will allow him to make the tallest model that will fit in the display case?

a)

1 inch = 10 feet

b)

1 inch = 15 feet

c)

1 inch = 17 feet

d)

1 inch = 20 feet

e)

1 inch = 25 feet

If you have some time to kill you can take the whole test

HERE It does take a little longer than the others though :)

The one above is killing me, because they will tell you whether or not you answered correctly, but they don't explain HOW to get the answer if you're wrong!

Anyway, I can't remember 8th grade math well enough to figure out the formula for this one.

I did do pretty well over all though :)